Cancer accounts for 8-9 million deaths a year, 80% of which are due to systemic spread of cancer to distant organs. It has long been recognized that primary cancers spread to distant organs with 'specific'preference, and skeleton/bone is one of the most common organs to be affected by metastatic cancer. Among primary cancers, prostate cancer is considered to be an orthotropic tumor with specific predilection to form bone metastasis. Over 70% of prostate cancer patients exhibit bone metastasis as detected during the disease course or autopsies. Prostate cancers are amongst the most commonly diagnosed malignancies and the 2nd leading cause of cancer death in men. Bone metastases are the predominant reason for prostate cancer related deaths, and current therapies have very short-term benefits, if any. To achieve the central objective, the laboratories of Kalluri, Pandolfi and Scadden have joined forces to propose a focused and cohesive plan to study the biology of bone metastasis. The three projects in this TMEN network will generate new genetic mouse models of metastatic prostate cancer, offer new insights into the biology of prostate cancer initiating cells, identify possible bone metastasis cell of origin, establish the role of tumor microenvironment in metastatic prostate cancer with specific emphasis on prostate and bone microenvironment, identify new therapeutic targets against metastatic prostate cancer and evaluate a new drugs for metastatic prostate cancer in pre-clinical trials. Successful completion of this proposed network proposal will offer significant new advances in area of metastatic prostate cancer.